1. Field of the Invention
The present invention relates to a mold for producing a thermoplastic resin molded article and to a process for producing a thermoplastic resin molded article using the mold.
2. Description of the Prior Art
A thermoplastic resin molded article and a multi-layer thermoplastic resin molded article wherein a skin material is integrally laminated to the entire or a part of a surface of a substrate comprising a thermoplastic resin have been used in various fields including automobile interior parts (for example, a door trim and an instrument panel) and interior and exterior parts of household electrical appliances.
Heretofore, as a process for producing such thermoplastic resin molded articles, a variety of processes, for example, injection molding, injection press molding and the like have been known.
In such processes, however, it is difficult to perfectly prevent in the molded article, uneven brightness which is called a cold mark or wrinkles which occur in a molded article surface corresponding to the vicinity of the resin-supplying opening. This is typically because a molten thermoplastic resin is supplied from a resin-supplying opening provided in a mold cavity surface for forming a molded article and is formed into a desired shape. Although it may be thought that the temperature of a resin or mold can be raised for the purpose of overcoming such a problem, this results in a long cooling time in that there arises another problem of deterioration in the productivity.
Further, as a process for producing a multi-layer thermoplastic resin molded article, there have been known, for example, a process in which a skin material is laminated by adhesion, using an adhesive or the like, onto a surface of a molded article (substrate) which has been prepared beforehand by forming a thermoplastic resin into a predetermined shape by injection molding or the like, and a process in which a skin material is supplied to between paired mold members, a molten thermoplastic resin is thereafter supplied to between the mold members, and the thermoplastic resin is then formed into a predetermined shape simultaneously when skin material is laminated to the surface of the shaped thermoplastic resin.
However, in such processes, the former includes complex procedures and has problems on human bodies, environment and the like caused by solvents contained in the adhesive. The latter has merit in that the formation of the substrate and the lamination of the skin material to a surface thereof can be achieved simultaneously. However, the latter has a problem in that when the molten thermoplastic resin is supplied from the resin-supplying opening provided in the mold, heat or supplying pressure to the molten thermoplastic resin causes a rip of the skin material. In the case of some types of skin materials, such a process causes crushing of a foamed layer which is a cushion layer, falling down of fuzz which induces the growth of unevenness in a surface of a product, an unsatisfactory feeling of cushion, difference in color, damage of texture and the like. Against such problems, there has been known a method for protecting a skin material from heat or supplying pressure at the time of resin supplying by providing a backing layer to a rear surface of the skin material. This method, however, has other problems of inducing poor shapability and mounting cost.
As a measure against these problems, there has been proposed a process using a mold in which a product-forming portion and a non-product-forming portion are interconnected with each other via a gate portion, the process comprising the steps of supplying a molten thermoplastic resin to the non-product-forming portion from a resin-supplying opening provided in the non-product-forming portion when the cavity clearance is not less than a thickness of a product to be formed, and closing the mold to form the molten thermoplastic resin (Japanese Patent Laid-Open Publication No. Hei 4-348919).
However, this method has a problem in that it is difficult for a non-product portion to be trimmed off from a product portion after molding since the gate portion, which connects the product-forming portion and the non-product-forming portion and functions as a resin path from the non-product-forming portion to the product-forming portion, has a constant thickness (FIGS. 5 and 11).
Under such circumstances, the present inventors have developed a mold for producing, in good efficiency and low cost, a thermoplastic resin molded article having a good surface appearance when a skin material is laminated as well as when no skin material is laminated thereto and having a non-product-forming portion which can readily be trimmed off from its product-forming portion after molding. They have also studied on a process for producing a thermoplastic resin molded article using the mold, and as a result, have reached the present invention.
The present invention provides a mold for producing a thermoplastic resin molded article, comprising paired female and male mold members wherein an outer peripheral surface of the male mold member and an inner peripheral surface of the female mold member, respectively, are sliding parts which mutually slide at the time of mold closing, and a product-forming portion and a non-product-forming portion, in the cavity thereof, in which said non-product-forming portion comprises a molten resin supplying opening at the mold surface thereof and said non-product-forming portion is interconnected to said product-forming portion by a gate portion which is a boundary between said non-product-forming portion and said product-forming portion, wherein at the time of mold closing, a width of said gate width at the product-forming-portion-side end of said gate portion, is less than the thickness of a product to be formed and continuously or stepwise widens from the boundary toward the non-product-forming-portion-side end of said gate portion. The present invention also provides a process for producing a thermoplastic resin molded article using the mold of the above 1, comprising closing the mold, while or after supplying molten thermoplastic resin, from the molten resin supplying opening, in an opened state, at the mold surface of the non-product-forming portion to between the male and female mold members, in an opened state, flowing the molten thermoplastic resin from the non-product-forming portion to the product-forming portion, packing the molten thermoplastic resin in the cavity, and cooling and solidifying the molten thermoplastic resin.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, and variations such as xe2x80x9ccomprisesxe2x80x9d and xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integer or step.